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How weight influences joint replacement surgery

For many years obese patients have been advised to shed weight before undergoing joint replacement surgery in the hope that some weight loss will reduce complications, aid faster recovery and lead to better outcomes. However, two studies into the question of how weight influences total knee replacement surgery recently presented at the 2013 Annual Meeting of the American Academy of Orthopaedic Surgeons, have produced some interesting results. The first, conducted in Singapore, found that there was little difference in the surgical outcomes between normal-weight and obese patients while the second, carried out in the United States, found that the cost of treating obese patients was significantly higher.

In Singapore, a team headed by Dr. Chin Tat Lim, of the University Orthopaedic Hand and Microsurgery Cluster at the National University Health System in Singapore, followed the fortunes of 301 patients – 77 obese (defined in the study as those with a body mass index (BMI) higher than 30) and 224 normal or overweight – for two years from the time just before surgery. The team found that, after taking sex, age and other health factors into account, obese patients did not suffer a significantly higher rate of surgical complications than the others. According to Dr. Lim this indicates that doctors need not withhold knee replacement surgery from obese patients, as they benefit in much the same way as non-obese patients.

These findings have, however, drawn criticism from Dr. Andrew Urquhart, associate professor of orthopaedic surgery at the University of Michigan Health System. He believes that the subject group was too small and, more important, there was no differentiation according to degrees of obesity and a BMI of 30, which would not necessarily be viewed as obese in the United States, was too low. These factors seriously distorted the results. He says that the risk of surgical complications increases as BMI increases. Dr Urquhart points out that for an individual who is 5 ft 6 in tall, a BMI of 30 would make them around 185 lbs; if their BMI was 40 they would be 247 lbs. The difference in weight changes the risk profile.

Dr. Urquhart was more supportive of a second study that investigated just over 8,000 patients, of whom around 75% had undergone total knee replacement surgery and 25% had had revision surgery at an American medical centre between January 2000 and September 2008.

This study, conducted by researchers at the Mayo Clinic in Rochester, corroborated the Singapore findings that obese patient faced no greater risk of complications than non-obese patients, but found that they remained in hospital for significantly longer periods.

The methodology was to divide the patients into eight groups according to BMI and, after considering age, type of surgery and general health, compare the costs associated with their surgery. It was found that patients with a lower BMI required shorter stays in hospital, those with a BMI lower than 35 needing the shortest. As BMI increased so the length of hospital stay increased along with the total cost of the treatment. For patients undergoing their first surgery, cost increased by $250-$300 for every five unit increase over in BMI over 30; this figure increased to $600-$650 for those having revision surgery.

According to Dr Hilal Maradit-Kremers, an associate professor of epidemiology at the Mayo Clinic and lead author of the study, total knee replacement surgery is one of the most common elective surgical procedures carried out in the United States. The study shows, therefore, that there is a huge hidden cost to the healthcare system caused by obesity.

Dr Maradit-Kremers’ team carried out similar studies on almost 9,000 who had had primary or revision hip replacement surgery. Its findings were similar to those in the knee replacement study. For every five unit increase in BMI over 30, the cost for patients having their first surgery increased by $500 for hospital costs and $900 in 90-day costs. These figures were around 60% higher for those having revision surgery.

Commenting on the Mayo Clinic studies, Dr. Urquhart said that they were impressive because paid regard to different degrees of obesity and supported anecdotal evidence regarding the care and treatment of patients as they increased in weight.

The bottom line, Dr. Urquhart believes, is that by losing weight before undergoing these elective procedures, obese patients will improve the surgical outcome as well as their general health. Often the fact that they want elective surgery gives them an incentive to shed weight they might otherwise lack. Irrespective, however, the difficult question of obesity needs to be addressed, particularly as there is a significant relationship between obesity and arthritis.

Matthew Morris. I am a PR consultant for Circle Partnership. Delivering the latest news and views from the industry is of huge importance to the consultancy.

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